1. Field of the Invention
The present invention relates to cathodes of lithium batteries and methods for fabricating the same and, particularly, to a carbon-nanotube-based cathode of a lithium battery and a method for fabricating the same.
2. Discussion of Related Art
In recent years, lithium batteries have received a great deal of attention.
Lithium batteries are used in various portable devices, such as notebook PCs, mobile phones, and digital cameras because of their small weight, high discharge voltage, long cyclic life, and high energy density compared with conventional lead storage batteries, nickel-cadmium batteries, nickel-hydrogen batteries, and nickel-zinc batteries.
A cathode of a lithium battery should have such properties as high energy density; high open-circuit voltage versus metallic lithium electrode; high capacity retention; good performance in common electrolytes; high density; good stability during charge and discharge processes, and low cost. Among various active materials, transition metal oxides and mixed transition metal oxides have received much attention owing to their relatively high charge/discharge capacities in the lithium batteries. At present, the most widely used cathode active materials are spinel type lithium manganese oxide (e.g. LiMn2O4), olivine type lithium iron phosphate (e.g. LiFePO4), and layered type lithium cobalt oxide (e.g. LiCoO2).
However, the low conductivity of the active materials generally induces a relatively large resistance in the cathode. As such, the charge/discharge depth of the lithium battery is relatively low. To decrease the resistance of the cathode, a conducting additive is commonly mixed with the active material. The weight of the conducting additive can reach to about 15%˜30% of the total weight of the cathode. If the conducting additive is increased and the weight of the battery must remain the same, the amount of active material in the cathode must be reduced, and thus, the energy density of the lithium battery will suffer.
To solve the above-described problem, carbon nanotubes as a novel conducting additive has been tested in cathodes of lithium batteries to take advantage of the excellent conductive properties thereof. In prior art, carbon nanotube powder is mixed with the active material by ultrasonically agitating. Unfortunately, carbon nanotubes are prone to aggregation due to the extremely large specific surface area thereof, and as such, aggregated carbon nanotubes will not improve the conductivity of the cathode.
What is needed, therefore, is to provide a cathode of a lithium battery and a method for fabricating the same, in which the above problems are eliminated or at least alleviated.